Data receiving status reporting method and apparatus

ABSTRACT

Embodiments provide a data receiving status reporting method and apparatus. The method includes: determining, by first user equipment, a status of receiving at least one packet data convergence protocol layer protocol data unit PDCP PDU by second user equipment, where the at least one PDCP PDU is forwarded by the first user equipment to the second user equipment after being received by the first user equipment through a communications link between the first user equipment and a network device; and sending, by the first user equipment, a first status report to the network device, where the first status report is used to indicate the status of receiving the at least one PDCP PDU by the second user equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/610,654, filed on Nov. 4, 2019, now U.S. Pat. No. 11,219,091, whichis a National Stage of International Application No. PCT/CN2017/083351,filed on May 5, 2017, each of which are hereby incorporated by referencein their entirety.

TECHNICAL FIELD

This application relates to the communications field, and in particular,to a data receiving status reporting method and an apparatus.

BACKGROUND

Currently, a first user equipment (“UE”) may establish a non-directcommunication path with a base station by using another user equipment,to perform data communication with the base station. This mode may bereferred to as a non-direct communication mode. In this case, the firstuse equipment may be referred to as “remote” UE, and the another userequipment may be referred to as “relay” UE.

In LTE Re1-15, data forwarding above a radio link control (“RLC”) layerand below a packet data convergence protocol (PDCP) layer of the relayUE is being researched. Such data forwarding may be referred to as Layer2 UE-to-NW Relay. In this case, the relay UE may be referred to as aLayer 2 relay UE.

When the remote UE communicates with the base station through anon-direct communication path of a Layer 2 UE-to-NW relay, the relay UEreceives downlink data sent by the base station, and forwards thedownlink data to the remote UE. However, the base station does not knowthe remote UE's status of receiving the downlink data, and thereforecontinues to send subsequent downlink data to the relay UE by using thenon-direct communication path of the Layer 2 UE-to-NW Relay. In reality,the remote UE may fail to receive some of the downlink data.Consequently, downlink data of the remote UE is lost.

Alternatively, after a communication path between the remote UE and thebase station is switched from the non-direct path to a direct path, thebase station does not know the remote UE's status of receiving thedownlink data sent by the base station to the remote UE by using thenon-direct path, and the base station continues to send subsequentdownlink data to the relay UE by using the direct communication path. Inreality, the remote UE may fail to receive some of the downlink data.Consequently, downlink data of the remote UE is lost.

SUMMARY

Embodiments provide a data receiving status reporting method andapparatus. When a communication path between a UE and a base station isto be switched from a non-direct path to a direct path, it can beensured that the UE sequentially receives downlink data sent by the basestation.

The following technical solutions are used in the embodiments to achievethe foregoing objective.

According to a first aspect, a data receiving status reporting method isdisclosed.

There is a direct path between a network device and first userequipment, and there is a non-direct path between the network device andsecond user equipment. The second user equipment communicates with thenetwork device through relay by the first user equipment. The first userequipment determines the second user equipment's status of receiving atleast one packet data convergence protocol (PDCP) layer protocol dataunit (PDU) (i.e., at least one PDCP PDU) by the second user equipment,where the at least one PDCP PDU is forwarded by the first user equipmentto the second user equipment after being received by the first userequipment through a communications link between the first user equipmentand the network device; and the first user equipment sends a firststatus report to the network device, where the first status report isused to indicate the status of the second user equipment receiving theat least one PDCP PDU.

When there is a non-direct path between the second user equipment and abase station, the base station sends at least one data packet (theforegoing at least one PDCP PDU) to the second user equipment by usingthe first user equipment. The first user equipment determines the seconduser equipment's status of receiving the at least one data packet by thesecond user equipment, and reports, to the base station, the status ofthe second user equipment receiving the at least one data packet. Whenthere is a direct path between the second user equipment and the basestation, the base station mays retransmit, in at least one data packetto the second user equipment based on a real status of receiving the atleast one data packet by the second user equipment, a data packet thatis not successfully received by the second user equipment. In exampleprior art, a status report fed back by the first user equipment to thebase station can only reflect a status of receiving the at least onedata packet by the first user equipment. If a packet loss occurs on atransmission path between the first user equipment and the second userequipment, the status report cannot reflect the real status of receivingthe at least one data packet by the second user equipment. However, inthis example embodiment, the status report that is fed back by the firstuser equipment and that is received by the base station can trulyreflect the status of receiving the at least one data packet by thesecond user equipment, and therefore out-of-order receiving by thesecond user equipment is avoided when the base station transmits a datapacket to the second user equipment based on the status report.

With reference to the example data receiving status reporting method, ina first possible implementation, the first status report includes firstinformation; and the first information is used to indicate a sequencenumber (“SN”) of a PDCP PDU that is in PDCP PDUs successfully forwardedby the first user equipment consecutively and that has a highest PDCPsequence number SN or a highest PDCP count value in the at least onePDCP PDU; or the first information is used to indicate a sequence numberSN of the last PDCP PDU that is in PDCP PDUs successfully forwarded bythe first user equipment consecutively in the at least one PDCP PDU; orthe first information is used to indicate a sequence number SN of a PDCPPDU following a PDCP PDU that is in PDCP PDUs successfully forwarded bythe first user equipment consecutively and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP PDU; or the firstinformation is used to indicate a sequence number SN of a PDCP PDUfollowing the last PDCP PDU that is in PDCP PDUs successfully forwardedb the first user equipment consecutively in the at least one PDCP PDU;or the first information is used to indicate a sequence number SN of aPDCP PDU that is in PDCP PDUs successfully received by the second userequipment consecutively and that has a highest PDCP SN or a highest PDCPcount value in the at least one PDCP PDU; or the first informationindicates a sequence number SN of the last PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively in theat least one PDCP PDU; or the first information is used to indicate asequence number SN of a PDCP PDU following a PDCP PDU that is in PDCPPDUs successfully received by the second user equipment consecutivelyand that has a highest PDCP SN or a highest PDCP count value in the atleast one PDCP PDU; or the first information is used to indicate asequence number SN of a PDCP PDU following the last PDCP PDU that is inPDCP PDUs successfully received by the second user equipmentconsecutively.

In this way, the first user equipment indicates, to the network device,the last PDCP PDU (or the PDCP PDU following the last PDCP PDU) that isin the PDCP PDUS successfully received by the second user equipmentconsecutively in the at least one. PDCP PDU. After receiving the firststatus report, the network device starts to transmit, to the second userequipment, the PDCP PDU following the last PDCP PDU that is in the PDCPPDUs successfully received by the second user equipment consecutively inthe at least one PDCP PDU. In this way, the second user equipment mayreceive a lost PDCP PDU in the at least one PDCP PDU before receiving aPDCP PDU following the at least one PDCP PDU sent by the network device,and therefore out-of-order receiving is avoided.

With reference to either the example data receiving status reportingmethod or the foregoing example implementation of the example datareceiving status reporting method, in a second possible exampleimplementation of the example data receiving status reporting method,the first status report includes second information; and the secondinformation is used to indicate a sequence number SN of a PDCP PDU thatis successfully forwarded by the first user equipment and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPPDU; or

the second information is used to indicate a sequence number SN of aPDCP PDU following a PDCP PDU that is successfully forwarded by thefirst user equipment and that has a highest PDCP SN or a highest PDCPcount value in the at least one PDCP PDU; or the second information isused to indicate a sequence number SN of a PDCP PDU that is successfullyreceived by the second user equipment and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP PDU; or the secondinformation is a sequence number SN of a PDCP PDU following a PDCP PDUthat is successfully received by the second user equipment and that hasa highest PDCP SN or a highest PDCP count value in the at least one PDCPPDU.

In this way, the first user equipment indicates, to the network device,the last PDCP PDU (or a PDCP PDU following the last PDCP PDU)successfully received by the second user equipment in the at least onePDCP PDU. After receiving the first status report, the network devicemay determine which PDCP PDU is the last one successfully received bythe second user equipment in the at least one PDCP PDU.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a third possible example implementation ofthe example data receiving status reporting method, the first statusreport further includes third information, and the third information isa PDCP sequence number of a lost PDCP PDU in the at least one PDCP PDUforwarded by the first user equipment to the second user equipment.

In this way, after receiving the first status report, in addition todetermining which PDCP PDU is last successfully received by the seconduser equipment in the at least one PDCP PDU, the network device maydetermine which PDCP PDU before or after the PDCP PDU has not beenreceived by the second user equipment. After receiving the first statusreport, the network device retransmits, to the second user equipment, aPDCP PDU that has not yet been received by the second user equipment inthe at least one PDCP PDU. In this way, the second user equipment mayreceive a lost PDCP PDU in the at least one PDCP PDU before receiving aPDCP PDU following the at least one PDCP PDU sent by the network device,and therefore out-of-order receiving is avoided.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a fourth possible implementation of theexample data receiving status reporting method, the first status reportincludes fourth information, and the fourth information is a sequencenumber SN of the first lost PDCP PDU in the at least one PDCP PDUforwarded by the first user equipment to the second user equipment orthe fourth information is a sequence number SN of the first PDCP PDUthat is not received by the second user equipment in the at least onePDCP PDU forwarded by the first user equipment to the second userequipment.

In this way, after the first user equipment sends the first statusreport to the network device, the network device may determine whichPDCP PDU in the at least one PDCP PDU is the first PDCP PDU that is notreceived by the second user equipment.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a fifth, possible implementation of theexample data receiving status reporting method, the first status reportfurther includes fifth information, and the fifth information is used toindicate a receiving status of a PDCP PDU after the first lost PDCP PDUor a receiving status of a PDCP PDU after the first PDCP PDU that is notreceived by the second user equipment.

In this way, the network device determines which PDCP PDU in the atleast one PDCP PDU is the first PDCP PDU that is not received by thesecond user equipment, and may further determine, based on the firststatus report, which PDCP PDU after the PDCP PDU is received by thesecond user equipment, and which PDCP PDU after the PDCP PDU is notreceived by the second user equipment. After a communication pathbetween the network device and the second user equipment is switched toa direct path, the network device first retransmits, to the second userequipment, a PDCP PDU that has not yet been received by the second userequipment in the at least one PDCP PDU. In this way, the second userequipment may receive a lost PDCP PDU in the at least one PDCP PDUbefore receiving a PDCP PDU following the at least one PDCP PDU sent bythe network device, and therefore out-of-order receiving is avoided.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a sixth possible implementation of theexample data receiving status reporting method, the first status reportfurther includes at least one of sixth information and seventhinformation; the sixth information is a user equipment identifier of thesecond user equipment; and the seventh information is a radio beareridentifier of the second user equipment.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a seventh possible implementation of theexample data receiving status reporting method, the first status reportis generated by one or more of an RLC layer, a PDCP, and an adaptationlayer between the PDCP and the RLC of the first user equipment.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in an eighth possible implementation of theexample data receiving status reporting method, before the first userequipment sends the first status report to the network device, themethod further includes: receiving, by the first user equipment, asecond status report sent by the second user equipment, where the secondstatus report is a radio link control (RLC) layer status report, and thesecond status report is used to indicate a status of receiving an RLCPDU by the second user equipment.

In other words, a trigger condition of the first status report may be“receiving a second status report sent by the second user equipment”.The first user equipment triggers and generates the first status reportonce the first user equipment receives the second status report sent bythe second user equipment.

With reference to any one of the example data receiving status reportingmethod or the foregoing implementations of the example data receivingstatus reporting method, in a ninth possible implementation of theexample data receiving status reporting method, that the first userequipment determines a status of receiving at least one PDCP PDU by thesecond user equipment specifically includes: the first user equipmentdetermines, based on the second status report, the status of receivingthe at least one PDCP PDU by the second user equipment.

According to a second aspect, an example apparatus is disclosed and isdisposed in user equipment, the user equipment is first user equipment,and the apparatus includes:

a determiner, configured to determine a status of receiving at least onepacket data convergence protocol layer protocol data unit PDCP PDU bysecond user equipment, where the at least one PDCP PDU is forwarded bythe first user equipment to the second user equipment by using atransmitter after being received by the first user equipment through acommunications link between the first user equipment and a networkdevice, where

the transmitter is father configured to send a first status report tothe network device, where the first status report is used to indicatethe status of receiving the at least one PDCP PDU by the second userequipment.

With reference to the example first user equipment apparatus, in a firstpossible implementation of the example first user equipment apparatus,the first status report includes first information; and the firstinformation is used to indicate a sequence number SN of a PDCP PDU thatis in PDCP PDUs successfully forwarded by the transmitter consecutivelyand that has a highest PDCP sequence number SN or a highest PDCP countcount value in the at least one PDCP PDU; or the first information isused to indicate a sequence number SN of the last PDCP PDU that is inPDCP PDUs successfully forwarded by the transmitter consecutively in theat least one PDCP PDU; or the first information is used to indicate asequence number SN of a PDCP PDU following a PDCP PDU that is in PDCPPDUs successfully forwarded by the transmitter consecutively and thathas a highest PDCP SN or a highest PDCP count value in the at least onePDCP PDU, or the first information is used to indicate a sequence numberSN of a PDCP PDU following the last PDCP PDU that is in PDCP PDUssuccessfully forwarded by the transmitter consecutively in the at leastone PDCP PDU; or the first information is used to indicate a sequencenumber SN of a PDCP PDU that is in PDCP PDUs successfully received bythe second user equipment consecutively and that has a highest PDCP PDUsor a highest PDCP count value in the at least one PDCP PDU; or the firstinformation indicates a sequence number SN of the last PDCP PDU that isin PDCP PDUs successfully received by the second user equipmentconsecutively in the at least one PDCP PDU; or the first information isused to indicate a sequence number SN of a PDCP PDU following a PDCP PDUthat is in PDCP PDUs successfully received by the second user equipmentconsecutively and that has a highest PDCP SN or a highest PDCP countvalue in the at least one PDCP PDU; or the first information is used toindicate a sequence number SN of a PDCP PDU following the last PDCP PDUthat is in PDCP PDUs successfully received by the second user equipmentconsecutively.

With reference to either the example first user equipment apparatus orthe foregoing possible implementation of the example first userequipment apparatus, in a second possible implementation of the examplefirst user equipment apparatus, the first status report includes secondinformation and the second information is used to indicate a sequencenumber SN of a PDCP PDU that is successfully forwarded by thetransmitter and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP PDU; or the second information is used toindicate a sequence number SN of a PDCP PDU following a PDCP PDU that issuccessfully forwarded by the transmitter and that has a highest PDCP SNor a highest PDCP count value in the at least one PDCP PDU; or thesecond information is used to indicate a sequence number of a PDCP PDUthat is successfully received by the second user equipment and that hasa highest PDCP SN or a highest PDCP count value in the at least one PDCPPDU; or the second information is a sequence number of a PDCP PDUfollowing a PDCP PDU that is successfully received by the second userequipment and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP PDU.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a third possible implementation of the examplefirst user equipment apparatus, the first status report further includesthird information, and the third information is a PDCP sequence numberSN of a lost PDCP PDU in the at least one PDCP PDU forwarded by thesending unit to the second user equipment.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a fourth possible implementation of the examplefirst user equipment apparatus, the first status report includes fourthinformation, and the fourth information is a sequence number of thefirst lost PDCP PDU in the at least one PDCP PDU forwarded by thetransmitter to the second user equipment; or the fourth information is asequence number SN of the first PDCP PDU that is not received by thesecond user equipment in the at least one PDCP PDU forwarded by thetransmitter to the second user equipment.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a fifth possible implementation of the examplefirst user equipment apparatus, the first status report further includesfifth information, and the fifth information is used to indicate areceiving status of a PDCP PDU after the first lost PDCP PDU or areceiving status of a PDCP PDU after the first PDCP PDU that is notreceived by the second user equipment.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a sixth possible implementation of the examplefirst user equipment apparatus, the first status report further includesat least one of sixth information and seventh information; the sixthinformation is a user equipment identifier of the second user equipment;and the seventh information is a radio bearer identifier of the seconduser equipment.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a seventh possible implementation of the examplefirst user equipment apparatus, the first status report is generated byone or more of an RLC layer, a PDCP, and an adaptation layer between thePDCP and the RLC of the apparatus.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in an eighth possible implementation of the examplefirst user equipment apparatus, the apparatus further includes areceiver, and the receiver is configured to: before the transmittersends the first status report to the network device, receive a secondstatus report sent by the second user equipment, where the second statusreport is a radio link control layer status report, and the secondstatus report is used to indicate a status of receiving an RLC PDU bythe second user equipment.

With reference to any one of the example first user equipment apparatusor the foregoing possible implementations of the example first userequipment apparatus, in a ninth possible implementation of the examplefirst user equipment apparatus, the determiner is specificallyconfigured to determine, based on the second status report, the statusof receiving the at least one PDCP PDU by the second user equipment.

According to a third aspect, a further example apparatus is disclosedand is disposed in user equipment, the user equipment is first userequipment, and the apparatus includes: a processor, configured todetermine a status of receiving at least one packet data convergenceprotocol layer protocol data unit PDCP PDU by second user equipment,where the at least one PDCP PDU is forwarded by the first user equipmentto the second user equipment by using a transmitter after being receivedby the first user equipment through a communications link between thefirst user equipment and a network device; and the transmitter,configured to send a first status report to the network device, wherethe first status report is used to indicate the status of receiving theat least one PDCP PDU by the second user equipment.

With reference to the further example first user equipment apparatus, ina first possible implementation of the further example first userequipment apparatus, the first status report includes first information;and the first information is used to indicate a sequence number SN of aPDCP PDU that is in PDCP PDUs successfully forwarded by the transmitterconsecutively and that has a highest PDCP sequence number SN or ahighest PDCP count count value in the at least one PDCP PDU; or thefirst information is used to indicate a sequence number SN of the lastPDCP PDU that is in PDCP PDUs successfully forwarded by the transmitterconsecutively in the at least one PDCP PDU; or the first information isused to indicate a sequence number SN of a PDCP PDU following a PDCP PDUthat is in PDCP PDUs successfully forwarded by the transmitterconsecutively and that has a highest PDCP SN or a highest PDCP countvalue in the at least one PDCP PDU; or the first information is used toindicate a sequence number SN of a PDCP PDU following the last PDCP PDUthat is in PDCP PDUs successfully forwarded by the transmitterconsecutively in the at least one PDCP PDU; or the first information isused to indicate a sequence number SN of a PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP PDU; or the first information indicates a sequence number SN ofthe last PDCP PDU that is in PDCP PDUs successfully received by thesecond user equipment consecutively in the at least one PDCP PDU; or thefirst information is used to indicate a sequence number SN of a PDCP PDUfollowing a PDCP PDU that is in PDCP PDUs successfully received by thesecond user equipment consecutively and that has a highest PDCP SN or ahighest PDCP count value in the at least one PDCP PDU; or the firstinformation is used to indicate a sequence number SN of a PDCP PDUfollowing the last PDCP PDU that is in PDCP PDUs successfully receivedby the second user equipment consecutively.

With reference to either the further example first user equipmentapparatus or the foregoing possible implementation of the furtherexample first user equipment apparatus, in a second possibleimplementation of the farther first user equipment example apparatus,the first status report includes second information; and the secondinformation is used to indicate a sequence number SN of a PDCP PDU thatis successfully forwarded by the transmitter and that has a highest PDCPSN or a highest PDCP count value in the at least one PDCP PDU; or thesecond information is used to indicate a sequence number SN of a PDCPPDU following a PDCP PDU that is successfully forwarded by thetransmitter and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP PDU; or the second information is used toindicate a sequence number SN of a PDCP PDU that is successfullyreceived by the second user equipment and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP PDU; or the secondinformation is a sequence number SN of a PDCP PDU following a PDCP PDUthat is successfully received by the second user equipment and that hasa highest PDCP SN or a highest PDCP count value in the at least one PDCPPDU.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample tint user equipment apparatus, in a third possibleimplementation of the further example first user equipment apparatus,the first status report further includes third information, and thethird information is a PDCP sequence number SN of a lost PDCP PDU in theat least one PDCP PDU forwarded by the transmitter to the second userequipment.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in a fourth possibleimplementation of the further example first user equipment apparatus,the first status report includes fourth information, and the fourthinformation is a sequence number SN of the first lost PDCP PDU in the atleast one PDCP PDU forwarded by the transmitter to the second userequipment; or the fourth information is a sequence number SN of thefirst PDCP PDU that is not received by the second user equipment in theat least one PDCP PDU forwarded by the transmitter to the second userequipment.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in a fifth possibleimplementation of the further example first user equipment apparatus,the first status report further includes fifth information, and thefifth information is used to indicate a receiving status of a PDCP PDUafter the first lost PDCP PDU ora receiving status of a PDCP PDU afterthe first PDCP PDU that is not received by the second user equipment.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in a sixth possibleimplementation of the further example first user equipment apparatus,the first status report further includes at least one of sixthinformation and seventh information; the sixth information is a userequipment identifier of the second user equipment; and the seventhinformation is a radio bearer identifier of the second user equipment.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in a seventh possibleimplementation of the further example first user equipment apparatus,the first status report is generated by one or more of an RLC layer, aPDCP, and an adaptation layer between the PDCP and the RLC of theapparatus.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in an eighth possibleimplementation of the further example first user equipment apparatus,the apparatus further includes a receiver, and

the receiver is configured to: before the transmitter sends the firststatus report to the network device, receive a second status report sentby the second user equipment, where the second status report is a radiolink control layer status report, and the second status report is usedto indicate a status of receiving an RLC PDU by the second userequipment.

With reference to any one of the further example first user equipmentapparatus or the foregoing possible implementations of the furtherexample first user equipment apparatus, in a ninth possibleimplementation of the further example first user equipment apparatus,the processor is specifically configured to determine, based on thesecond status report, the status of receiving the at least one PDCP PDUby the second user equipment.

According to a fourth aspect, a further example data receiving statusreporting method is disclosed and includes:

determining, by second user equipment, a status of receiving at leastone PDCP SDU by the second user equipment, where the at least one PDCPSDU is forwarded by first user equipment to the second user equipmentafter being received by the first user equipment through acommunications link between the first user equipment and a networkdevice; and sending, by the second user equipment, a status report tothe network device, where the status report is used to indicate thestatus of receiving the at least one PDCP SDU by the second userequipment.

With reference to the further example data receiving status reportingmethod, in a first possible implementation of the further example datareceiving status reporting method, the status report includes firstinformation; and the first information is used to indicate a sequencenumber SN of a PDCP SDU that is in PDCP SDUs successfully forwarded bythe first user equipment consecutively and that has a highest PDCPsequence number SN or a highest PDCP count count value in the at leastone PDCP SDU; or the first information is used to indicate a sequencenumber SN of the last PDCP SDU that is in PDCP SDUs successfullyforwarded by the first user equipment consecutively in the at least onePDCP SDU; or the first information is used to indicate a sequence numberSN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfullyforwarded by the first user equipment consecutively and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPSDU; or the first information is used to indicate a sequence number SNof a PDCP SDU following the last PDCP SDU that is in PDCP SDUssuccessfully forwarded by the first user equipment consecutively in theat least one PDCP SDU; or the first information is used to indicate asequence number SN of a PDCP SDU that is in PDCP SDUs successfullyreceived by the second user equipment consecutively and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPSDU; or the first information indicates a sequence number SN of the lastPDCP SDU that is in PDCP SDUs successfully received by the second userequipment consecutively in the at least one PDCP SDU; or the firstinformation is used to indicate a sequence number SN of a PDCP SDUfollowing a PDCP SDU that is in PDCP SDUs successfully received by thesecond user equipment consecutively and that has a highest PDCP SN or ahighest PDCP count value in the at least one PDCP SDU; or the firstinformation is used to indicate a sequence number SN of a PDCP SDUfollowing the last PDCP SDU that is in PDCP SDUs successfully receivedby the second user equipment consecutively.

With reference to either the further example data receiving statusreporting method or the foregoing possible implementation of the furtherexample data receiving status reporting method, in a second possibleimplementation of the further example data receiving status reportingmethod, the status report includes second information; and

the second information is used to indicate a sequence number SN of aPDCP SDU that is successfully forwarded by the first user equipment andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP SDU or the second information is used to indicate a sequencenumber SN of a PDCP SDU following a PDCP SDU that is successfullyforwarded by the first user equipment and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP SDU; or the secondinformation is used to indicate a sequence number SN of a PDCP SDU thatis successfully received by the second user equipment and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPSDU; or the second information is a sequence number SN of a PDCP SDUfollowing a PDCP SDU that is successfully received by the second userequipment and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP

With reference to any one of the further example data receiving statusreporting, method or the foregoing possible implementations of thefurther example data receiving status reporting method, in a thirdpossible implementation of the further example data receiving statusreporting method, the status report further includes third information,and the third information is a PDCP sequence number SN of a lost PDCPSDU in the at least one PDCP SDU forwarded by the first user equipmentto the second user equipment.

With reference to any one of the further example data receiving statusreporting method or the foregoing possible implementations of thefurther example data receiving status reporting method, in a fourthpossible implementation of the further example data receiving statusreporting method, the status report includes fourth information, and thefourth information is a sequence number SN of the first lost PDCP SDU inthe at least one PDCP SDU forwarded by the first user equipment to thesecond user equipment; or the fourth information is a sequence number SNof the first PDCP SDU that is not received by the second user equipmentin the at least one PDCP SDU forwarded by the first user equipment tothe second user equipment.

With reference to any one of the further example data receiving statusreporting method or the foregoing possible implementations of thefurther example data receiving status reporting method, in a sixthpossible implementation of the further example data receiving statusreporting method, the status report further includes fifth information,and the fifth information is used to indicate a receiving status of aPDCP SDU after the first lost PDCP SDU or a receiving status of a PDCPSDU after the first PDCP SDU that is not received by the second userequipment.

With reference to any one of the further example data receiving statusreporting method or the foregoing possible implementations of thefurther example data receiving status reporting method, in a seventhpossible implementation of the further example data receiving statusreporting method, the status report is generated by a PDCP of the seconduser equipment.

According to a fifth aspect, an example apparatus is disclosed and isdisposed in user equipment, the user equipment is second user equipment,and the apparatus includes:

a processor, configured to determine a status of receiving at least onepacket data convergence protocol layer protocol data unit PDCP PDU bythe second user equipment, where the at least one PDCP PDU is forwardedby first user equipment to the second user equipment after beingreceived by the first user equipment through a communications linkbetween the first user equipment and a network device; and atransmitter, configured to send a status report to the network device,where the status report is used to indicate the status of receiving theat least one PDCP PDU by the second user equipment.

According to a sixth aspect of the example embodiments, a non-transitorycomputer storage medium is disclosed, and is configured to store acomputer software instruction that is used by the foregoing apparatusdisposed in the first user equipment. The computer software instructionincludes a program used to perform the example data receiving statusreporting method in the first aspect.

According to a seventh aspect of the example embodiments, anothernon-transitory computer storage medium is disclosed, and is configuredto store a computer software instruction that is used by the foregoingapparatus disposed in the second user equipment. The computer softwareinstruction includes a program used to perform the further example datareceiving status reporting method in the fourth aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a prior art schematic diagram of two existing operating modesof communication between UE and a base station;

FIG. 2 is a schematic diagram of prior an existing radio interfaceprotocol layer;

FIG. 3A and FIG. 3B are a schematic diagram of a prior art end-to-endprotocol stack in an existing non-direct communication mode;

FIG. 4 is a schematic structural diagram of an apparatus according to anexample embodiment;

FIG. 5 is a schematic flowchart of a data receiving status reportingmethod according to an example embodiment;

FIG. 6 a is a schematic diagram of a frame structure of a first statusreport according to an example embodiment;

FIG. 6 b is a schematic diagram of another frame structure of a firststatus report according to an example embodiment;

FIG. 7 a is a schematic diagram of another frame structure of a firststatus report according to an example embodiment;

FIG. 7 b is a schematic diagram of another frame structure of a firststatus report according to an example embodiment;

FIG. 8 a is a schematic diagram of another frame structure of a firststatus report according to an example embodiment;

FIG. 8 b is a schematic diagram of another frame structure of a firststatus report according to an example embodiment;

FIG. 9 is a schematic flowchart of another data receiving statusreporting method according to an example embodiment;

FIG. 10 is another schematic structural diagram of an apparatusaccording to an example embodiment;

FIG. 11 is another schematic structural diagram of an apparatusaccording to an example embodiment;

FIG. 12 is another schematic structural diagram of an apparatusaccording to an example embodiment;

FIG. 13 is another schematic structural diagram of an apparatusaccording to an example embodiment; and

FIG. 14 is another schematic structural diagram of an apparatusaccording to an example embodiment.

DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1 , there may be the following two modes for aconnection between UE and a base station 1. The UE is directly connectedto the base station to perform data communication. This manner may bereferred to as a direct communication mode. In this case, there is adirect path between the UE and the base station.

2. One user equipment is connected to the base station by using anotheruser equipment to perform data communication. This mode may be referredto as a non-direct communication mode. In this case, the first userequipment may be referred to as remote user equipment (remote UE), theanother user equipment may be referred to as relay user equipment (relayUE), and there is a non-direct path between the remote UE and the basestation. In addition or alternative to a 3GPP sidelink/PC5 accesstechnology, the remote UE and the relay UE may be connected by using anon-3GPP access technology, for example, a Bluetooth access technologyor a WLAN access technology.

Referring to FIG. 2 , in an LTE system, a radio interface includes aradio resource control (“RRC”) protocol layer, a packet data convergenceprotocol (“PDCP”) layer, a radio link control (“RLC”) protocol layer,and a media access control (“MAC”) protocol layer.

The RRC layer processes layer 3 information of a control plane betweenUE and a base station.

The PDCP layer is responsible for compressing and decompressing an IPheader. On a user plane, after obtaining IP data packets from an upperlayer, the PDCP layer may perform header compression and encryption onthe IP data packets, maintain a sequence number (SN) for each obtaineddata packet, and then sequentially deliver the data packets to the RLClayer.

The RLC layer mainly performs segmentation and/or concatenation on thereceived upper-layer data packet, so that data packets obtained afterthe segmentation and/or concatenation are suitable for actualtransmission on the radio interface. In addition, for a radio bearer(“RB”) that requires errorless transmission, the RLC layer protocol mayfurther recover a lost data packet by using a retransmission mechanism.For example, at a transmit end, the RLC layer receives PDCP PDUs whoseSNs are 0, 1, and 2 and that are transmitted by the PDCP layer, and mayperform segmentation and/or concatenation on the three PDCP PDUs toobtain two RLC PDUs whose numbers are 0 and 1. At a receive end, the RLClayer may perform segmentation and/or concatenation on the received RLCPDUs to obtain the three PDCP PDUs whose SNs are 0, 1, and 2.

The MAC layer defines how a data frame is transmitted on a medium.

In the non-direct communication mode shown in FIG. 1 , when the remoteUE is connected to a network by using the relay UE, and the remote UE isconnected to the relay UE by using the 3GPP access technology, anend-to-end protocol stack of a user plane corresponding to the remote UEis shown in FIG. 3A and FIG. 3B. An interface of a link between therelay UE and the remote UE is referred to as PC5, and a correspondinglink is a sidelink. An interface of a link between the relay UE and thebase station is Uu, and a corresponding link includes a downlink or anuplink. Referring to FIG. 3A and FIG. 3B, at a transmit end (forexample, the base station), each layer receives a service data unit(SDU) from a higher layer, and outputs a protocol data unit (PDU) to alower layer. For example, an RLC (Uu) of the base station receivespackets from a PDCP (Uu) of the base station. These packets are PDCPPDUs from the perspective of the PDCP, or are RLC SDUs from theperspective of the RLC. At a receive end (for example, the relay UE),this process is in reverse. Each layer sends an SDU to an upper layer,and the upper layer receives the SDU as a PDU. For example, a PDCP (Uu)of the relay UE receives packets from an RLC (Uu) of the relay UE. Thesepackets are PDCP PDUs from the perspective of the PDCP, or are RLC SDUsfrom the perspective of the RLC.

Usually, different RLC modes may be configured for each RLC entity (forexample, an RLC (Uu) and an RLC (PC5) in FIG. 3A and FIG. 3B) dependingon service types. The RLC modes specifically include a transparent mode(“TM”), an unacknowledged mode (“UM”), and an acknowledged mode (“AM”).When the RLC mode of the RLC entity is configured as the AM, an RLCentity on a sending side first sequentially concatenates pre-bufferedRLC service data units (SDUs) to obtain a data field in an RLC PDU basedon a transmission opportunity notified by the media access control (MAC)layer and a size of a data packet that can be sent; constructs headerinformation corresponding to the data field based on a protocolrequirement, where the data field and the header information form acomplete RLC PDU; and then sends the RLC PDU to an RLC entity on areceiving side. The header information of the RLC PDU includes one SN,and the SN is increased by 1 each time one new RLC PDU is sent.

In addition, after receiving some RLC PDUs, the RLC entity on thereceiving side sends art RLC status report to the RLC entity on thesending side according to a feedback mechanism, where the status reportincludes an SN of an RLC PDU that is to be retransmitted by the RLCentity on the sending side. After receiving the status report, the RLCentity on the sending side is to retransmit, based on the currenttransmission opportunity and the size of the data packet that can besent, the RLC PDU that is to be retransmitted.

Referring to FIG. 1 , the remote UE may switch between two connectionmodes or two communication paths. For example, when quality of a linkbetween UE and the base station is relatively poor, the UE may choose toconnect to the base station by using nearby relay UE. In this case,switching from the direct communication mode to the non-directcommunication mode is performed. For another example, when the relay UEconnected to the remote UE moves, a connection between the remote UE andthe relay UE may no longer be maintained. In this case, switching fromthe non-direct communication mode to the direct communication mode isperformed.

In downlink data transmission, the base station first sends, to therelay UE, data that is to be sent to the remote UE. RLC (Uu) entity ofthe relay UE sends an RLC status report to the base station. The RLCstatus report is carried on an RLC status PDU. For a format of the RLCstatus PDU, refer to the radio link control (RLC) protocol specificationin Ts 36.322. The status report includes a receiving status of an RLCPDU. After receiving the status report fed back by the RLC entity of therelay UE, the base station may determine, based on the status report, anRLC sequence number of an RLC PDU that has been successfully received bythe relay UE and an RLC sequence number of a lost RLC PDU. Based on thesequence number SN of the RLC PDU and a segmentation status and aconcatenation status of the RLC SDU during data sending, the basestation may determine an RLC SDU of the remote UE successfully receivedby the relay UE and a lost RLC SDU, and may further determine a PDCPsequence number of a PDCP PDU/PDCP SDU of the remote UE successfullyreceived by the relay UE.

After the relay UE forwards data of the remote UE to the remote UE, anRLC (PC5) entity of the remote UE feeds back an RLC status report to anRLC (PC5) entity of the relay UE. After receiving the status report fedback by the RLC entity of the remote UE, the relay UE may determine,based on the status report, an RLC sequence number SN of an RLC PDU thathas been successfully received by the remote UE and an RLC sequencenumber of a lost PDU. Based on the sequence number SN of the RLC PDU anda segmentation status and a concatenation status of the RLC SDU duringdata sending, the relay UE may determine an RLC SDU of the remote UEsuccessfully received by the remote UE and a lost RLC SDU, and mayfurther determine a PDCP sequence number of a PDCP PDU/PDCP SDUsuccessfully received by the remote UE in PDCP PDUs/PDCP SDUs that areto be sent by the base station to the remote UE, and a sequence numberSN of a lost PDCP PDU/PDCP SDU of the remote UE in the PDCP PDUs/PDCPSDUs that are to be sent by the base station to die remote UE.

However, in a process of transmitting downlink data in the non-directcommunication mode, the base station cannot know a PDCP sequence numberSN of a PDCP PDU/PDCP SDU of the remote UE successfully received by theremote UE in the data sent to the remote UE and a sequence number SN ofa lost PDCP PDU/PDCP SDU of the remote UE. Consequently, downlink dataof the remote UE is lost. Specifically, there may be the following threecases:

Case 1: In a process in which the base station normally transmitsdownlink data by using the non-direct communication path, because thebase station does not know a transmission status of data between therelay UE and the remote UE, a communication rate of the link between thebase station and the relay UE may be far higher than a communicationrate of the link between the relay UE and the remote UE. Therefore, therelay UE is to buffer a large quantity of data packets forwarded to theremote UE. When the amount of data packets that are to be bufferedexceed a buffer capability of the relay UE, the relay UE discards anextra data packet. Consequently, a downlink data packet of the remote UEis lost.

Case 2: The base station forwards the downlink data of the remote UE byusing the relay UE. After the base station sends the data to the relayUE, the base station may know, based on a status report fed back by anRLC layer of the relay UE, which downlink data has been correctlyreceived by the relay UE, and which data has not been received by therelay UE. However, the base station does not know which data packetsforwarded by the relay UE have been successfully received by the remoteUE, and which data packets have not been successfully received by theremote UE. Based on the status report fed back by the RLC layer of therelay UE, the base station may clear, from a sending buffer, a datapacket that has been correctly received by the relay UE. In this way,after the communication path between the remote UE and the base stationis switched from the non-direct path to the direct path (in other words,the remote UE is directly connected to the base station forcommunication), because the relay UE cannot forward the downlink data tothe remote UE, the remote UE can receive, only from the base stationdata that has not been successfully received. In this case, for datapackets that have been cleared by the base station from the sendingbuffer but have not been correctly received by the remote UE, the remoteUE cannot obtain these data packets from the base station by using thedirect path. Consequently, a downlink data packet of the remote UE islost.

Case 3: After the remote UE is switched from the non-direct path to thedirect path (in other words, the remote UE is directly connected to thebase station for communication), downlink PDCP SDUs received from thebase station may be received out of order. However, in a normal datareceiving process, a PDCP layer of the remote UE directly delivers thereceived PDCP SDUs to an upper layer without reordering the receivedPDCP SDUs. Therefore, data packets delivered by the PDCP to the upperlayer are out-of-order. Out-of-order delivery to the upper layer maylead to a data packet loss at the upper layer.

A feature of this example embodiment is as follows: When there is anon-direct path between the remote UE and the base station, the basestation sends at least one data packet to the remote UE by using therelay UE, and the relay UE determines a status of receiving the at leastone data packet by the remote UE, and reports, to the base station, thestatus of receiving the at least one data packet by the remote UE.Alternatively, when there is a non-direct path between the remote UE andthe base station, the base station sends at least one data packet to theremote UE by using the relay UE, and the remote UE reports a receivingstatus of the at least one data packet to the base station.

In this way, based on a status that is of receiving downlink data by theremote UE and that is reported by the relay UE or a receiving status ofdownlink data that is reported by the remote UE, the base station maydetermine which downlink data transmitted to the remote UE by using therelay UE has been successfully received by the remote UE, and whichdownlink data has not been successfully received by the remote UE.

For the foregoing Case 1, in a process of transmitting data in thenon-direct communication mode, the base station may adjust atransmission rate of the link between the base station and the relay UEbased on a status of receiving a downlink data packet by the remote UE,thereby avoiding a packet loss in Case 1.

For the foregoing Case 2, in a process of transmitting data in thenon-direct communication manner, the base station may determine, basedon a status of receiving a downlink data packet by the remote UE, whichdata packets may be deleted from the sending buffer. Therefore, afterthe remote UE is switched from the non-direct path to the direct path, apacket loss in Case 2 is avoided.

For the foregoing Case 3, after the remote UE is switched from thenon-direct path to the direct path, the base station may sequentiallyperform retransmission based on a status of receiving a downlink datapacket by the remote UE. Therefore, the PDCP the remote UE alsosequentially receives data, and sequentially delivers the received datato a higher layer. Therefore, a packet loss in Case 3 can be avoided.

In a specific example implementation, FIG. 4 is a schematic compositiondiagram of user equipment according to an example embodiment. The userequipment may be the first user equipment in the embodiments, or may bethe relay user equipment in the communications system shown in FIG. 1 .As shown in FIG. 4 , the user equipment may include at least oneprocessor 11, a memory 12, a communications interface 13, acommunications interface 15, and a communications bus 14.

Constituent parts of the user equipment are described in detail belowwith reference to FIG. 4 .

The processor 11 is a control center of the user equipment, and may beone processor, or may be a collective name of a plurality of processingelements. For example, the processor 11 is a central processing unit(CPU), or may be an application-specific integrated circuit (ASIC), ormay be configured as one or more integrated circuits implementing thisembodiment for example, one or more microprocessors, digital signalprocessors (DSPs) or one or more field programmable gate arrays (FPGAs).

The processor 11 may implement various functions of the user equipmentby running or executing a software program stored in the non-transitorymemory 12 and invoking data stored in the memory 12.

In specific implementation, as an embodiment, the processor 11 mayinclude one or more CPUs, for example, a CPU 0 and a CPU 1 shown in FIG.4 .

In a specific example implementation, the user equipment include aplurality of processors, for example, the processor 11 and a processor15 shown in FIG. 4 . Each of these processors may be a single-coreprocessor (single-CPU), or may be a multi-core processor (multi-CPU).The processor herein may be one or more devices, circuits, and/orprocessing cores used to process data (such as a computer programinstructions).

The memory 12 may be a read-only memory (read-only memory, ROM), anothertype of static storage device that may store static information andinstructions, a random access memory (RAM), or another type of dynamicstorage device that may store information and instructions; or may be anelectrically erasable programmable read-only memory (EEPROM), a compactdisc read-only memory (CD-ROM) or another optical disk storage, anoptical disc storage (including a compact optical disc, a laser disc, anoptical disc, a digital versatile disc, a Blu-ray disc, and the like), amagnetic disk storage medium or another magnetic storage device, or anyother medium that can be configured to carry or store program code in aform of an instruction or a data structure and that can be accessed by acomputer. This does not constitute a limitation herein. The memory 12may exist independently, and is connected to the processor 11 throughthe communications bus 14. Alternatively, the memory 12 may beintegrated with the processor 11.

The memory 12 is configured to store a software program, and theprocessor 11 controls execution of the software program.

The communications interface 13 and the communications interface 15 areconfigured to communicate, by using any apparatus such as a transceiver,with another device or a communications network such as an Ethernet, aradio access network (RAN), or a wireless local area network (WLAN). Thecommunications interface 13 is a communications interface between a UEand a network device, and the communications interface 15 is acommunications interface between a relay UE and a remote UE. Thecommunications interface 13 and the communications interface 15 mayinclude a receiver for implementing a receiving function and atransmitter or sender for implementing a sending function.

The communications bus 14 may be an industry standard architecture (ISA)bus, a peripheral component interconnect (PCI) bus, an extended industrystandard architecture (EISA) bus, or the like. The bus may be classifiedinto an address bus, a data bus, a control bus, and the like. For easeof indication, the bus is indicated by using only one bold line in FIG.4 . However, the single line does not indicate that there is only onebus or only one type of bus.

The structure of the device shown in FIG. 4 does not constitute alimitation on the user equipment. The user equipment may include more orfewer components than those shown in the diagram, combine somecomponents, or have different component arrangements.

In some example embodiments, the communications interface 13 receives,by using a data radio bearer (DRB) between the communications interface13 and the network device, at least one PDCP PDU sent by the networkdevice to second user equipment. The network device herein may be a basestation, for example, the base station in the communications systemshown in FIG. 1 . The second user equipment herein may be user equipmentthat is not directly connected to the base station and that is tocommunicate with the base station through relay by the first userequipment, for example, the relay user equipment in the communicationssystem shown in FIG. 1 .

Subsequently, the communications interface 15 forwards the at least onePDCP PDU tee the second user equipment by using a sidelink radio bearer(SL-RB) or a non-3GPP link between the first user equipment (userequipment in which the apparatus shown in FIG. 4 is disposed) and thesecond user equipment.

When the first user equipment is connected to the second user equipmentby using a sidelink technology, further, after receiving some RLC PDUsthat carry the PDCP PDU forwarded by the first user equipment, an RLCentity of the second user equipment sends an RLC status report (a secondstatus report in this example embodiment) to the first user equipment,to indicate a status of receiving the RLC PDU by the second userequipment. The communications interface 15 of the first user equipmentreceives the second status report. It should be noted that an RLC entityof the communications interface 15 of the first user equipment, namely,an RLC entity (referred to as a first RLC entity of the first userequipment below) of a radio bearer of a sidelink between the first userequipment and the second user equipment, may perform segmentation and/orconcatenation on a received PDCP PDU/RLC SDU that is to be forwarded tothe second user equipment, to obtain an RLC PDU, and then forward theRLC PDU to the second user equipment. Therefore, the second userequipment reports a receiving status of the RLC PDU. For example, for anRLC PDU, if a receiving status of the RLC PDU in an RLC status reportreported by the second user equipment is acknowledge (ACK), it indicatesthat the RLC PDU is successfully received by the second user equipment.On the contrary, if a receiving status of the RLC PDU in an RLC statusreport is not acknowledge (NACK), it indicates that the RLC PDU is notsuccessfully received by the second user equipment. In other words, thesecond user equipment fails to receive the RLC PDU.

After receiving the RLC status report sent by the second user equipment,the first user equipment may determine, based on the status of receivingthe RLC PDU by the second user equipment, a status of receiving the atleast one PDCP PDU by the second user equipment. In a specific exampleimplementation, the processor 11 of the first user equipment determines,based on the status of receiving the RLC PDU by the second userequipment, the status of receiving the at least one PDCP PDU by thesecond user equipment. Specifically, the RLC entity of the first userequipment performs segmentation and/or concatenation on the at least onePDCP PDU/RLC SDU to obtain an RLC PDU, and then forwards the RLC PDU tothe second user equipment. Therefore, the first user equipment maydetermine, based on the status of receiving the RLC PDU by the seconduser equipment, the status of receiving the at least one PDCP PDU by thesecond user equipment. For example, the first RLC entity of the firstuser equipment receives PDCP PDUs, whose PDCP SNs are 0, 1, and 2, thatare transmitted by an adaptation layer entity of the first userequipment and that are to be forwarded to the second user equipment. Theadaptation layer is above an interface between the first user equipmentand the network device in FIG. 3A and FIG. 3B. Based on a size of anavailable transmission resource on the sidelink, the first RLC entity ofthe first user equipment may perform segmentation and/or concatenationon the three PDCP PDUs/RLC SDUs to obtain two RLC PDUs whose RLC numbersare 0 and 1. If receiving statuses of the two RLC PDUs whose numbers are0 and 1 in an RLC status report fed back by the second user equipmentare ACK, the two RLC PDUs are successfully received by the second userequipment, and the first user equipment may determine that all the threePDCP PDUs whose SNs are 0, 1, and 2 are successfully received by thesecond user equipment.

The first user equipment may generate a first status report based on thestatus of the second user equipment receiving the at least one PDCP PDUand that is determined based on the second status report, and send thefirst status report to the network device through the communicationsinterface 13, where the first status report is used to indicate thestatus of the second user equipment receiving the at least one PDCP PDU.

The first status report is triggered in the following three ways:

2. After receiving the second status report, the first user equipmenttriggers and generates the first status report. Specifically, afterreceiving the second status report, the first RLC entity of the firstuser equipment determines, based on the second status report, the statusof receiving the at least one PDCP PDU by the second user equipment, andnotifies the adaptation layer entity above the interface between thefirst user equipment and the network device of the receiving status. Theadaptation layer entity triggers and generates the second status report.

2. The first user equipment periodically triggers the first statusreport. The period length is configured by the base station.Specifically, the first user equipment maintains at least one timer.When the first user equipment receives the period length configured bythe base station, the first user equipment starts the timer. When thetimer expires, the adaptation layer entity of the first user equipmenttriggers and generates the first status report. For the timer, the firstuser equipment may maintain a common timer for second user equipmentconnected to the first user equipment. When the timer expires, the firstuser equipment triggers and generates first status reports of all radiobearers of all the second user equipment. Alternatively, the first userequipment maintains one timer for each second user equipment connectedto the first user equipment. When the timer expires, the first userequipment triggers and generates first status reports of all radiobearers of corresponding second user equipment; or the first userequipment maintains one timer for each radio bearer of each second userequipment connected to the first user equipment. When the timer expires,the first user equipment triggers and generates a first status report ofa corresponding radio bearer of corresponding second user equipment.

3. The first user equipment triggers the first status report based onindication information of the base station. After the first userequipment receives the indication information of the base station, theadaptation layer entity of the first user equipment triggers a firststatus report of a corresponding radio bearer of corresponding seconduser equipment. In an example implementation, the indication is includedin an adaptation layer PDU sent by the base station to the first userequipment. The indication may be 1-bit information. For example, the 1bit may be referred to as a poll bit. In addition, the adaptation layerPDU sent by the base station to the first user equipment furtherincludes a second user equipment identifier corresponding to theadaptation layer PDU and a radio bearer identifier of the second userequipment. When a value of the 1-bit information in the adaptation layerPDU received by the first user equipment is set to 1, it indicates thatthe first user equipment is to trigger the first status report of thecorresponding radio bearer of the corresponding second user equipment.However, when a value of the 1-bit information in the adaptation layerPDU received by the first user equipment is set to 0, it indicates thatthe first user equipment does not trigger the first status report of thecorresponding radio bearer of the corresponding second user equipment,or vice versa.

In the foregoing description, the first status report is triggered bythe adaptation layer, However, if the adaptation layer is not anindependent protocol layer, but serves as a sub-layer or a sub-functionmodule of a PDCP layer between the first user equipment and the seconduser equipment, the first status report is finally triggered by the PDCPlayer, and correspondingly, the first status report is about a PDCP PDU.

In addition, the first status report may be alternatively triggered byan RLC layer between the first user equipment and the second userequipment, and correspondingly, the first status report is about an RLCPDU.

The following describes information included in the first status reportin detail with reference to an example. In specific implementation, thefirst status report is implemented in the following four ways.

First, it is assumed that the base station is to forward 10 PDCP PDUswhose SNs are sequentially 0 to 9 to the second user equipment by usingthe first user equipment. The first user equipment determines, based onthe second status report fed back by the second user equipment, that thesecond user equipment receives PDCP PDUs whose SNs are 0 to 5 and a PDCPPDU whose SN is 9. In other words, the second user equipment finis toreceive PDCP PDUs whose SNs are 6 to 8.

1. In some embodiments, the first status report includes firstinformation, and the first information is used to indicate a sequencenumber SN of a PDCP PDU that is in PDCP PDUs successfully forwarded bythe first user equipment consecutively and that has a highest PDCPsequence number SN or a highest PDCP count value in the at least onePDCP PDU. “Consecutively successful forwarding” may be understood asthat N PDCP PDUs successfully forwarded in ascending order of SNs areconsecutive, and there is no lost PDCP PDU in the N PDCP PDUs duringforwarding. In addition, “successful forwarding” means that the seconduser equipment receives a PDCP PDU forwarded by the first userequipment. In the foregoing example, the first user equipment determinesthat SNs of PDCP PDUs received by the second user equipment are 0, 1, 2,3, 4, 5, and 9. Therefore, SNs of PDCP PDUs successfully forwarded bythe first user equipment are 0, 1, 2, 3, 4, 5, and 9. Further, “asequence number of a PDCP PDU that is in PDCP PDUs successfullyforwarded by the first user equipment consecutively and that has ahighest PDCP sequence number SN or a highest PDCP count value” is 5.

Alternatively, the first information is used to indicate a sequencenumber SN the last PDCP PDU that is in PDCP PDUs successfully forwardedby the first user equipment consecutively in the at least one PDCP PDU.In the foregoing example, the first user equipment determines that SNsof PDCP PDUs received by the second user equipment are 0, 1, 2, 3, 4, 5,and 9. Therefore, “a sequence number of the last PDCP PDU that is inPDCP PDUs successfully forwarded by the first user equipmentconsecutively” is 5.

Alternatively, the first information is used to indicate a sequencenumber of a PDCP PDU following a PDCP PDU that is in PDCP PDUssuccessfully forwarded by the first user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP PDU. In the foregoing example, the first user equipmentdetermines that SNs of PDCP PDUs received by the second user equipmentare 0, 1, 2, 3, 4, 5, and 9, and “a sequence number of the last PDCP PDUthat is in PDCP PDUs successfully forwarded by the first user equipmentconsecutively” is 5. Therefore, “a sequence number of a PDCP PDUfollowing a PDCP PDU that is in PDCP PDUs successfully forwarded by thefirst user equipment consecutively and that has a highest PDCP SN or ahighest PDCP count value” is 6.

Alternatively, the first information is used to indicate a sequencenumber SN of a PDCP PDU following the last PDCP PDU that is in PDCP PDUssuccessfully forwarded by the first user equipment consecutively in theat least one PDCP PDU. In the foregoing example, the first userequipment determines that SNs of PDCP PDUs received by the second userequipment are 0, 1, 2, 3, 4, 5, and 9, and “the last PDCP PDU that is inPDCP PDUs successfully forwarded by the first user equipmentconsecutively” is 5. Therefore, “a sequence number of a PDCP PDUfollowing the last PDCP PDU that is in PDCP PDUs successfully forwardedby the first user equipment consecutively” is 6.

Alternatively, the first information is used to indicate a sequencenumber SN of a PDCP PDU that is in PDCP PDUs successfully received bythe second user equipment consecutively and that has a highest PDCP SNor a highest PDCP count value in the at least one PDCP PDU. In theforegoing example, the first user equipment determines that SNs of PDCPPDUs received by the second user equipment are 0, 1, 2, 3, 4, 5, and 9,and SNs of PDCP PDUs successfully received by the second user equipmentconsecutively are 0, 1, 2, 3, 4, and 5. Therefore, “a sequence number ofa PDCP PDU that is in PDCP PDUs successfully forwarded by the first userequipment consecutively and that has a highest PDCP sequence number SNor a highest PDCP count value” is 5.

Alternatively, the first information indicates a sequence number SN ofthe last PDCP PDU that is in PDCP PDUs successfully received by thesecond user equipment consecutively in the at least one PDCP PDU. In theforegoing example, the first user equipment determines that SNs of PDCPPDUs received by the second user equipment are 0, 1, 2, 3, 4, 5, and 9,and SNs of PDCP PDUs successfully received by the second user equipmentconsecutively are 0, 1, 2, 3, 4, and 5. Therefore, “a sequence number ofthe last PDCP PDU that is in PDCP PDUs successfully received by thesecond user equipment consecutively” is 5.

Alternatively, the first information is used to indicate a sequencenumber SN of a PDCP PDU following a PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP PDU. In the foregoing example, the first user equipmentdetermines that SNs of PDCP PDUs received by the second user equipmentare 0, 1, 2, 3, 4, 5, and 9, and SNs of PDCP PDUs successfully receivedby the second user equipment consecutively are 0, 1, 2, 3, 4, and 5. Asequence number of the PDCP PDU that is in the PDCP PDUs successfullyreceived by the second user equipment consecutively and that has thehighest PDCP SN or the highest PDCP count value is 5. Therefore, “asequence number of a PDCP PDU following a PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count value” is 6.

Alternatively, the first information is used to indicate a sequencenumber SN of a PDCP PDU following the last PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively. In theforegoing example, the first user equipment determines that SNs of PDCPPDUs received by the second user equipment are 0, 1, 2, 3, 4, 5, and 9,and SNs of PDCP PDUs successfully received by the second user equipmentconsecutively are 0, 1, 2, 3, 4, and 5. A sequence number of the lastPDCP PDU that is in the PDCP PDUs successfully received by the seconduser equipment consecutively is 5. Therefore, “a sequence number of aPDCP PDU fallowing the last PDCP PDU that is in PDCP PDUs successfullyreceived by the second user equipment consecutively” is 6.

2. In some embodiments, the first status report includes secondinformation. The second information is used to indicate a sequencenumber SN of a PDCP PDU that is successfully forwarded by the first userequipment and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP PDU. In the foregoing example, the first userequipment determines that SNs of PDCP PDUs received by the second userequipment are 0, 1, 2, 3, 4, 5, and 9. In other words, SNs of PDCP PDUssuccessfully forwarded by the first user equipment are 0, 2, 3, 4, 5,and 9. Therefore, “a sequence number of a PDCP PDU that is successfullyforwarded by the first user equipment and that has a highest PDCP SN ora highest PDCP count value” is 9.

Alternatively, the second information is used to indicate a sequencenumber SN of a PDCP PDU following a PDCP PDU that is successfullyforwarded by the first user equipment and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP PDU. In theforegoing example, the first user equipment determines that SNs of PDCPPDUs received by the second user equipment are 0, 1, 2, 3, 4, 5, and 9.In other words, SNs of PDCP PDUs successfully forwarded by the firstuser equipment are 0, 1, 2, 3, 4, 5, and 9. Therefore, “a sequencenumber of a PDCP PDU following a PDCP PDU that is successfully forwardedby the first user equipment and that has a highest PDCP SN or a highestPDCP count value” is 10.

Alternatively, the second information is used to indicate a sequencenumber SN of a PDCP PDU that is successfully received by the second userequipment and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP PDU. In the foregoing example, the first userequipment determines that SNs of PDCP PDUs received by the second userequipment are 0, 1, 2, 3, 4, 5, and 9. Therefore, “a sequence number ofa PDCP PDU that is successfully received by the second user equipmentand that has a highest PDCP SN or a highest PDCP count value” is 9.

Alternatively, the second information is a sequence number SN of a PDCPPDU following a PDCP PDU that is successfully received by the seconduser equipment and that has a highest PDCP SN or a highest PDCP countvalue in the at least one PDCP PDU. In the foregoing example, the firstuser equipment determines that SNs of PDCP PDUs received by the seconduser equipment are 0, 1, 2, 3, 4, 5, and 9. “A sequence number of a PDCPPDU that is successfully received by the second user equipment and thathas a highest PDCP SN or a highest PDCP count value” is 5. Therefore, “asequence number of a PDCP PDU following a PDCP PDU that is successfullyreceived by the second user equipment and that has a highest PDCP SN ora highest PDCP count value” is 10.

Further, the second information is used to indicate a PDCP PDU with ahighest sequence number SN in PDCP PDUs received by the second userequipment, and further indicate a receiving status of a PDCP PDU whosesequence number SN is lower than that of the PDCP PDU, for example,indicating which PDCP PDU whose sequence number is lower than that ofthe PDCP PDU is lost or is not received by the second user equipment.The first status report further includes third information, and thethird information is used to indicate a PDCP sequence number of a lostPDCP PDU in the at least one PDCP PDU forwarded by the first userequipment to the second user equipment. It should be noted that the“lost PDCP PDU” may be considered as a PDCP PDU that is to be receivedbut is not received by the second user equipment. In the foregoingexample, the first user equipment determines that SNs of PDCP PDUsreceived by the second user equipment are 0, 1, 2, 3, 4, 5, and 9, andSNs of lost PDCP PDUs are 6, 7, and 8. Therefore, the third informationis used to indicate the sequence numbers 6, 7, and 8.

3. In some embodiments, the first status report includes fourthinformation, and the fourth information is a sequence number SN of thefirst lost PDCP PDU in the at least one PDCP PDU forwarded by the firstuser equipment to the second user equipment. In the foregoing example,the first user equipment determines that SNs of PDCP PDUs received bythe second user equipment are 0, 1, 2, 3, 4, 5, . . . , and 9, and SNsof lost PDCP PDUs are 6, 7, and 8 in a process of forwarding from thefirst user equipment to the second user equipment. Therefore, it isdetermined that “a sequence number of the first lost PDCP PDU in the atleast one PDCP PDU forwarded by the first user equipment to the seconduser equipment” is 6.

Alternatively, the fourth information is a sequence number SN of thefirst PDCP PDU that is not received by the second user equipment in theat least one PDCP PDU forwarded by the first user equipment to thesecond user equipment. In the foregoing example, the first userequipment determines that SNs of PDCP PDUs received by the second userequipment are 0, 1, 2, 3, 4, 5, . . . , and 9, and SNs of PDCP PDUS ofthe second user equipment are 6, 7, and 8 in a process of forwardingfrom the first user equipment to the second user. Therefore, it isdetermined that “a sequence number of the first PDCP PDU that is notreceived by the second user equipment in the at least one PDCP PDU” is6.

Further, after the first lost PDCP PDU in all PDCP PDUs received by thesecond user equipment is indicated by using the fourth information, areceiving status of a PDCP PDU after the PDCP PDU, namely, a receivingstatus of a PDCP PDU whose sequence number is higher than that of thePDCP PDU, is further indicated. Specifically, the first status reportfurther includes fifth information, and the fifth information is used toindicate a receiving status of a PDCP PDU after the first lost PDCP PDUor a receiving status of a PDCP PDU after the first PDCP PDU that is notreceived by the second user equipment. In the foregoing example, thefifth information is used to indicate a receiving status of a PDCP PDUafter the first lost PDCP PDU, namely, a PDCP PDU whose sequence numberis 6. In some embodiments, “0” may be used to indicate that the seconduser equipment fails to receive a PDP PDU, and “1” may be used toindicate that the second user equipment receives a PDCP PDU. Herein, thefifth information may be “001”, where the first “0” indicates that thesecond user equipment fails to receive a PDCP PDU whose SN is 7, thesecond “0” indicates that the second user equipment fails to receive aPDCP PDU whose SN is 8, and the last “1” indicates that the second userequipment receives a PDCP PDU whose SN is 9.

4. In some embodiments, the first status report includes sixthinformation, and the sixth information is a sequence number of the firstlost PDCP PDU in the at least one PDCP PDU forwarded by the first userequipment to the second user equipment. In the foregoing example, thefirst user equipment determines that SNs of PDCP PDUs received by thesecond user equipment are 0, 1, 2, 3, 4, 5, and 9, and SNs of lost PDCPPDUs are 6, 7, and 8 in a process of forwarding from the first userequipment to the second user equipment. Therefore, it is determined that“a sequence number of the first lost PDCP PDU in the at least one PDCPPDU forwarded by the first user equipment to the second user equipment”is 6.

Alternatively, the sixth information is a sequence number SN of thefirst PDCP PDU that is not received by the second user equipment in theat least one PDCP PDU forwarded by the first user equipment to thesecond user equipment. In the foregoing example, the first userequipment determines that SNs ref PDCP PDUs received by the second userequipment are 0, 1, 2, 3, 4, 5, . . . , and 9, and SNs of PDCP PDUs ofthe second user equipment are 6, 7, and 8 in a process of forwardingfrom the first user equipment to the second user. Therefore, it isdetermined that “a sequence number of the first PDCP PDU that is notreceived b the second user equipment in the at least one PDCP PDU” is 6.

Further, after the first lost PDCP PDU in all PDCP PDUs received by thesecond user equipment is indicated by using the sixth information, asequence number SN of a PDCP PDU that is successfully forwarded by thefirst user equipment and that has a highest PDCP SN or a highest PDCPcount value in the at least one PDCP PDU and a quantity of lost PDCPPDUs is further indicated. Specifically, the first status report furtherincludes seventh information and eighth information, where the seventhinformation is used to indicate a sequence number of a PDCP PDU that issuccessfully forwarded by the first user equipment and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPPDU, and the eighth information is used to indicate a quantity of lostPDCP PDUs.

In the foregoing example, “a sequence number of a PDCP PDU that issuccessfully forwarded by the first user equipment and that has ahighest PDCP SN or a highest PDCP count value” is 9, and the quantity oflost PDCP PDUs is 3.

It should be noted that, in addition to the foregoing information, thefirst status report in the foregoing four implementations may includeinformation indicating a buffer size of the first user equipment. Theinformation about the buffer size may be a size of a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a total butallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment.

An example embodiment provides a data receiving status reporting method.As shown in FIG. 5 , the method includes the following steps.

101. First user equipment receives at least one PDCP PDU sent by anetwork device.

Referring to FIG. 1 , there is a non-direct path between a base stationand a second user, the second user equipment is connected to the firstuser equipment, and the second user equipment may receive, through relayby the first user equipment, downlink data sent by the base station.Therefore the base station first sends, to the first user equipment byusing a corresponding second radio bearer, at least one PDCP PDU that isfrom a first radio bearer and that is to be sent to the second userequipment. The first radio bearer is a radio bearer between the seconduser equipment and the network device. As shown in FIG. 3A and FIG. 3B,the first radio bearer includes a PDCP entity between the second userequipment and the network device. The second radio hearer is a radiobearer between the first user equipment and the network device. As shownin FIG. 3A and FIG. 3B, the second radio bearer includes an RLC (Uu)entity between the first user equipment and the network device and acorresponding logical channel.

102. The first user equipment forwards the at least one PDCP PDU to asecond user.

In a specific example implementation, when the first user equipment isconnected to the second user equipment by using a sidelink technology,the first user equipment may send the at least one PDCP PDU to thesecond user equipment by using a third radio bearer of a sidelinkbetween the first user equipment and the second user equipment. Thethird radio bearer is a radio bearer between the first user equipmentand the second user equipment. As shown in FIG. 3A and FIG. 3B, thethird radio hearer includes an RLC (PC5) entity between the first userequipment and the second user equipment and a corresponding logicalchannel. Optionally, the third radio bearer further includes a PDCP(PC5) entity between the first user equipment and the second userequipment.

103. The first user equipment determines a status of receiving the atleast one PDCP PDU by the second user equipment.

It should be noted that, limited to a network status of transmissionbetween the first device and the second device, the second userequipment may fail to receive some PDCP PDUs the at least one PDCP PDU.To avoid a packet loss, the second user equipment is to feed back thereceiving status of the at least one PDCP PDU to the first userequipment, so that the first user equipment retransmits, based on thefed-back receiving status, a PDCP PDU that is not correctly received bythe second user equipment.

104. The first user equipment sends a first status report to the networkdevice, where the first status report is used to indicate the status ofreceiving the at least one PDCP PDU by the second user equipment.

Trigger of the first status report has the foregoing threepossibilities, and details are not described herein again.

Implementation of the first status report has the foregoing threepossibilities, and specific carried content is not further describedherein. The following uses an example in which the first status reportis carried on an adaptation layer PDU to describe content and a formatincluded in the first status report.

A first example implementation of the first status report may have aformat of the form shown in FIG. 6 a . For example, a length of a PDCPSN is 7 bits. Another length of the PDCP SN may be correspondinglydesigned. Referring to FIG. 6 a , a data/control (Date/Control, D/C)field is used to indicate whether a current adaptation layer PDU is adata PDU or a control PDU.

A PDU type (type) field is used to indicate a type of a control PDU if acurrent adaptation layer PDU is the control PDU. For example, 000represents a type of a PDU. Other values (001 to 111) currently may bereserved values.

A UE local ID field is used to indicate a unique identifier of remote UE(the second user equipment in this example embodiment) connected torelay UE. In other words, the UE local ID field may be a uniqueidentifier of the second user equipment connected to the first userequipment. For example, three user equipment are relayed by the firstuser equipment, where 00 represents user equipment A, 01 represents userequipment B, and 10 represents user equipment C (the second userequipment in this embodiment). In this case, the UF local ID field ispadded with 10.

An RB ID field is used to indicate a DRB of remote UE to which a currentstatus report is specific, namely, a radio bearer identifier of thethird radio bearer.

An R field is used to indicate a reserved bit.

An HDS (highest successfully delivered in sequence PDCP SN) field isused to indicate am SN corresponding to a PDCP PDU that has a highestPDCP SN and that is in PDCP PDUs with consecutive SNs successfullytransmitted by the relay UE (the first user equipment in thisembodiment) to the remote UE by using the third radio bearer indicatedby the RB ID field, namely, first information in this embodiment, forexample, a sequence number SN of a PDCP PDU that is in PDCP PDUssuccessfully forwarded by the first user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count in the at least onePDCP PDU. Certainty, the HDS field may be alternatively used to indicateanother sequence number SN in the foregoing first implementation, forexample, a sequence number of a PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count in the at least onePDCP PDU.

It should be noted that, as shown in FIG. 6 b , the first status reportshown in FIG. 6 a may further include a buffer indication fieldbuffersize, and the buffer indication field buffersize is used toindicate information about a buffer size of the first user equipment.The information about the buffer size may be a size of a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment.

The buffer indication field of 4 bytes is used as an example in FIG. 6 b. A different length may be designed, and this is not limited herein.

In the foregoing example, the base station forwards 10 PDCP PDUs whoseSNs are sequentially 0 to 9 to the second user equipment by using thefirst user equipment. The first user equipment determines, based on asecond status report fed back by the second user equipment, that thesecond user equipment receives PDCP PDUs whose SNs are 0 to 5 and a PDCPPDU whose SN is 9. In other words, the second user equipment fails toreceive PDCP PDUs whose SNs are 6 to 8. A value of the HDS field may be5 or 6.

In conclusion, the first status report defined in the firstimplementation may be implemented in the format shown in FIG. 6 a orFIG. 6 b.

In a second example implementation of the first status report, a formatof the first status report may be a form shown in FIG. 7 a . Referringto FIG. 7 a , for functions of a D/C field, a PDU type field, a UE localID field, an RB field, and an R field, refer to the foregoingdescriptions of these indication fields in FIG. 6 a . Details are notdescribed herein again.

In addition, an ACK_SN field is used to indicate an SN corresponding toa PDCP PDU that has a highest PDCP SN or a highest PDCP count and thatis in PDCP PDUs successfully transmitted by the relay UE to the remoteUE by using the third radio bearer indicated by the RB ID field, namely,“second information” in the second implementation, for example, “asequence number of a PDCP PDU that is successfully forwarded by thefirst user equipment and that has a highest PDCP SN or a highest PDCPcount value in the at least one PDCP PDU” in this embodiment. Certainly,the ACK_SN field may be alternatively used to indicate another sequencenumber in the foregoing first implementation, for example, a sequencenumber of a PDCP PDU following a PDCP PDU that is in PDCP PDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count in the at least onePDCP PDU.

A NACK_SN field is used to indicate an SN corresponding to a PDCP PDUthat has not been successfully transmitted by the relay UE to the remoteUE, namely, third information in this embodiment, and may be a PDCPsequence number of a lost PDCP PDU in the at least one PDCP PDUforwarded by the first user equipment to the second user equipment.

It should be noted that, as shown in FIG. 7 b , the first status reportshown in FIG. 7 a may further include a buffer indication fieldbuffersize, and the buffer indication field buffersize is used toindicate information about a buffer size of the first user equipment.The information about the buffer size may be a size of a total bufferallocated by the first user equipment to the second user equipment: or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment.

In addition, the buffer indication field of 4 bytes is used as anexample in FIG. 7 b . Another length may be designed, and this is notlimited herein.

It should be noted that a quantity of lost PDCP PDUs in the at least onePDCP PDU is equal to a quantity of NACK_SN fields, and each NACK_SNfield is filled with an SN of a lost PDCP PDU. In the foregoing example,the base station forwards 10 PDCP PDUs whose SNs are sequentially 0 to 9to the second user equipment by using the first user equipment. Thefirst user equipment determines, based on a second status report fedback by the second user equipment, that the second user equipmentreceives PDCP PDUs whose SNs are 0 to 5 and a PDCP PDU whose SN is 9. Inother words, the second user equipment fails to receive PDCP PDUs whoseSNs are 6 to 8. A value of the ACK_SN field is 9, and values of theNACK_SN fields are sequentially 6, 7, and 8.

In conclusion, the first status report defined in the secondimplementation may be implemented in the format shown in FIG. 7 a orFIG. 7 b.

In a third example implementation of the first status report, a formatof the first status report may be a form shown in FIG. 8 a . Referringto FIG. 8 a , for functions of a D/C field, a PDU type field, a UE localID field, an RB ID field, and an R field, refer to the foregoingdescriptions of these indication fields in FIG. 6 a . Details are notdescribed herein again.

In addition, an FUDS (First undelivered PDCP SN) field is used toindicate a sequence number SN corresponding to the first PDCP PDU thathas not been successfully transmitted by the relay UE to the remote UEby using the third radio bearer indicated by the RB field, namely,fourth information in this embodiment, for example, “a sequence numberof the first lost PDCP PDU in the at least one PDCP PDU forwarded by thefirst user equipment to the second user equipment”.

A bitmap field is used to indicate a receiving status of a PDCP PDUafter a PDCP PDU indicated by the FUDS field. Specifically, the bitmapfield is used to indicate a PDCP PDU after a PDCP PDU indicated by oneFUDS field corresponding to each bit in the bitmap field, and is used toindicate whether a PDCP PDU corresponding to the bit has beensuccessfully sent to the remote UE. For example, in this exampleembodiment, “1” indicates that the second user equipment receives acorresponding PDCP PDU forwarded by the first user equipment, and “0”indicates that the second user equipment fails to receive acorresponding PDCP PDU forwarded by the first user equipment.

It should be noted that, a quantity of bits in the bitmap field in thefirst status report shown in FIG. 8 is equal to a quantity of PDCPsequence numbers between the last PDCP PDU successfully received by thesecond user equipment and a PDCP PDU following the first lost PDCP PDUin PDCP PDUs that are forwarded by the first user equipment to thesecond user equipment by using, the third radio bearer indicated by theRB ID field. In addition, each bit is filled with a value indicating areceiving status of one PDCP PDU, for example, “0” or “1”. In theforegoing example, the base station is to forward 10 PDCP PDUs whose SNsare sequentially 0 to 9 to the second user equipment by using the firstuser equipment. The first user equipment determines, based on a secondstatus report fed back by the second user equipment, that the seconduser equipment receives PDCP PDUs whose SNs are 0 to 5 and a PDCP PDUwhose SN is 9. In other words, the second user equipment fails toreceive PDCP PDUs whose SNs are 6 to 8. A value of the FUDS field is 6,and values of bitmap fields are sequentially 0, 0, and 1.

It should be noted that, as shown in FIG. 8 b , the first status reportshown in FIG. 8 a may further include a buffer indication fieldbuffersize, and the buffer indication field buffersize is used toindicate information about a buffer size of the first user equipment.The information about the buffer size may be a size of a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a total bufferallocated by the first user equipment to the second user equipment; or

the information about the buffer size is a size of a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment: or

the information about the buffer size is a size of an available bufferat a reporting moment of the first status report in a buffer that isallocated by the first user equipment to the second user equipment tostore data of each radio bearer of the second user equipment.

In addition, the buffer indication field of 4 bytes is used as anexample in FIG. 8 b . Another length may be designed, and this is notlimited herein.

In conclusion, the first status report defined in the third exampleimplementation may be implemented in the format shown in FIG. 8 a orFIG. 8 b.

It should be noted that in this embodiment, a PDCP PDU after a PDCP PDUis a PDCP PDU whose PDCP sequence number SN or PDCP count value ishigher than that of the PDCP PDU. In addition, a PDCP PDU before thePDCP PDU is a PDCP PDU whose PDCP sequence number or PDCP count value istower than that of the PDCP PDU.

An example embodiment further provides a data receiving status reportingmethod. As shown in FIG. 9 , the method includes the following steps.

201. First user equipment receives at least one PDCP PDU sent by anetwork device.

Referring to FIG. 1 , there is a non-direct path between a base stationand a second user, the second user equipment is connected to the firstuser equipment, and the second user equipment may receive, through relayby the first user equipment, downlink data sent by the base station.Therefore, the base station first sends, to the first user equipment byusing a corresponding second radio bearer, at least one PDCP PDU that isfrom a first radio bearer and that is to be sent to the second userequipment. The first radio bearer is a radio bearer between the seconduser equipment and the network device. As shown in FIG. 3A and FIG. 3B,the first radio bearer includes a PDCP entity between the second userequipment and the network device. The second radio bearer is a radiobearer between the first user equipment and the network device. As shownin FIG. 3A and FIG. 3B, the second radio bearer includes an RLC (Uu)entity between the first user equipment and the network device and acorresponding logical channel.

202. The first user equipment forwards the at least one PDCP PDU to asecond user.

In a specific example implementation, when the first user equipment isconnected to the second user equipment by using a sidelink technology,the first user equipment may send the at least one PDCP PDU to thesecond user equipment by using a third radio bearer of a sidelinkbetween the first user equipment and the second user equipment. Thethird radio bearer is a radio bearer between the first user equipmentand the second user equipment. As shown in FIG. 3A and FIG. 3B, thethird radio bearer includes an RLC (PC5) entity between the first userequipment and the second user equipment and a corresponding logicalchannel. Optionally, the third radio bearer further includes a PDCP(PC5) entity between the first user equipment and the second userequipment.

203. The second user equipment determines a receiving status of the atleast one PDCP PDU.

In a specific example implementation, an RLC entity of the first userequipment performs segmentation and/or concatenation on the at least onePDCP PDU to obtain an RLC PDU, and then forwards the RLC PDU to thesecond user equipment. Alternatively, an RLC layer of the second userequipment may perform segmentation and/or concatenation on a receivedRLC PDU to obtain a PDCP PDU, and then deliver the obtained PDCP PDU toa PDCP layer of the second user equipment. Therefore, the PDCP layer ofthe second user equipment may determine which PDCP PDU in the at leastone PDCP PDU is received by the second user equipment, and which PDCPPDU is not received by the second user equipment.

For example, the RLC entity of the first user equipment receives PDCPPDUs whose SNs are 0, 1, and 2 and that are transmitted by a PDCP entityof the first user equipment, and may perform concatenation on the threePDCP PDUs to obtain two RLC PDUs whose numbers are 0 and 1. If receivingstatuses of the two RLC PDUs whose numbers are 0 and 1 in an RLC statusreport fed back by the second user equipment are ACK, the two RLC PDUsare successfully received by the second user equipment, and the firstuser equipment may determine that all the three PDCP PDUs whose SNs are0, 1, and 2 are successfully received by the second user equipment.

204. The second user equipment sends a status report to the networkdevice, where the status report is used to indicate the status ofreceiving the at least one PDCP PDU by the second user equipment.

It should be noted that implementations of the status report reported bythe second user equipment may be the same as the foregoing fourimplementations of the first status report.

When the second user equipment determines the status report in theforegoing first implementation, a PDCP entity of the second userequipment determines first information in the first status report basedon a currently received PDCP SDU (which may be considered as a PDCP PDUin this embodiment).

In some embodiments, a trigger condition of the status report is: whenan RLC entity of the second user equipment triggers the RLC statusreport, the RLC entity of the second user equipment instructs the PDCPentity to trigger the status report. For example, referring to FIG. 3Aand FIG. 3B, when a PC5 RLC entity of remote UE triggers sending of theRLC status report, the PC5 RLC entity instructs a PDCP entity (a PDCP(Uu) shown in FIG. 3A and FIG. 3B) to trigger the status report.

Alternatively the base station configures a sending period of the statusreport for the remote UE (the second user equipment in this embodiment).The remote UE starts a timer, and when the periodic timer expires, aPDCP entity of the remote UE triggers the status report. For the timer,the second user equipment may maintain a common timer for all thirdradio bearers. When the timer expires, the second user equipmenttriggers and generates PDCP status reports of all the third radiobearers. Alternatively, the second user equipment maintains one timerfor each third radio bearer. When the tinier expires, the second userequipment triggers and generates a PDCP status report of a correspondingthird radio bearer.

Alternatively, when the PDCP entity of the remote UE receives a PDCP PDUsent by the base station, and an indicator bit (Poll bit) included inthe PDCP PDU instructs the remote UE to trigger the PDCP status report,the PDCP entity triggers the status report. For example, when a value ofthe indicator bit (Poll bit) included in the PDCP PDU is 1 “0”, the PDCPentity of the remote UE does not trigger the status report; or when thePDCP PDU includes “1”, the PDCP entity of the remote UE triggers thestatus report.

When the second user equipment determines the status report in theforegoing second, fourth, or fourth implementation of the first statusreport, the second user equipment may determine the status report byusing the following two methods.

1. After the PDCP entity of the second user equipment triggers thestatus report, the PDCP entity queries the RLC entity of the second userequipment about a receiving status of a PDCP PDU. After receiving thequery indication, the RLC entity performs segmentation and/orconcatenation on RLC PDUs that are received out of order, and determinesa sequence number SN of a PDCP PDU corresponding to an RLC SDU that isobtained through segmentation and/or concatenation.

Specifically, for example, when the PDCP triggers the status report, andqueries the RLC entity about the receiving status of the PDCP PDU, RLCnumbers of RLC PDUs currently received by the RLC are 6, 7, and 8.Before this, the RLC has received RLC PDUs whose RLC numbers are 1, 2,and 3, and delivered the RLC PDUs to the PDCP entity. Because RLC PDUswhose RLC numbers are 4, 5, and 6 are not received, the RLC entity doesnot deliver the RLC PDUs whose RLC numbers are 6, 7, and 8 to the PDCPentity. After receiving the query indication from the PDCP, the RLClayer performs segmentation and/or concatenation on the RLC PDUs whosenumbers are 6, 7, and 8. For example, two RLC SDUs are obtained afterthe segmentation and/or concatenation, and numbers of PDCP PDUsrespectively corresponding to the two RLC SDUs are 4 and 5. In thiscase, the RLC notifies the PDCP layer that PDCP PDUs whose PDCP SNs are4 and 5 have been successfully received, so that the PDCP layerdetermines content of the PDCP status report.

2. When the remote UE is connected to the base station in a non-directmode, a reordering function is no longer performed by an RLC entity ofthe remote UE, but is performed by a PDCP entity. In this way, the PDCPentity can obtain, in a timely manner, an SN of a PDCP PDU that has beensuccessfully received.

It should be noted that in this example the status report determined bythe PDCP of the second user equipment includes the first information.

The first information is used to indicate a sequence number SN of a PDCPSDU that is in PDCP SDUs successfully forwarded by the first userequipment consecutively and that has a highest PDCP sequence number SNor a highest PDCP count value in the at least one PDCP SDU; or the firstinformation is used to indicate a sequence number of the last PDCP SDUthat is in PDCP SDUs successfully forwarded by the first user equipmentconsecutively in the at least one PDCP SDU; or the first information isused to indicate a sequence number SN of a PDCP SDU following a PDCP SDUthat is in PDCP SDUs successfully forwarded by the first user equipmentconsecutively and that has a highest PDCP SN or a highest PDCP countvalue in the at least one PDCP SDU; or the first information is used toindicate a sequence number SN of a PDCP SDU following the last PDCP SDUthat is in PDCP SDUs successfully forwarded by the first user equipmentconsecutively in the at least one PDCP SDU; or the first information isused to indicate a sequence number SN of a PDCP SDU that is in PDCP SDUssuccessfully received by the second user equipment consecutively andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP SDU; or the first information indicates a sequence number SN ofthe last PDCP SDU that is in PDCP SDUs successfully received by thesecond user equipment consecutively in the at least one PDCP SDU; or thefirst information is used to indicate a sequence number SN of a PDCP SDUfollowing a PDCP SDU that is in PDCP SDUs successfully received by thesecond user equipment consecutively and that has a highest PDCP SN or ahighest PDCP count value in the at least one PDCP SDU; or the firstinformation is used to indicate a sequence number SN of a PDCP SDUfollowing the last PDCP SDU that is in PDCP SDUs successfully receivedby the second user equipment consecutively.

In some embodiments, the status report includes second information, andthe second information is used to indicate a sequence number SN of aPDCP SDU that is successfully forwarded by the first user equipment andthat has a highest PDCP SN or a highest PDCP count value in the at leastone PDCP SDU; or the second information is used to indicate a sequencenumber SN of a PDCP SDU following a PDCP SDU that is successfullyforwarded by the first user equipment and that has a highest PDCP SN ora highest PDCP count value in the at least one PDCP SDU; or the secondinformation is used to indicate a sequence number SN of a PDCP SDU thatis successfully received by the second user equipment and that has ahighest PDCP SN or a highest PDCP count value in the at least one PDCPSDU; or the second information is a sequence number SN of a PDCP SDUfollowing a PDCP SDU that is successfully received by the second userequipment and that has a highest PDCP SN or a highest PDCP count valuein the at least one PDCP SDU.

If the status report includes the second information, the status reportfurther includes third information. The third information is a PDCPsequence number SN of a lost PDCP SDU in the at least one PDCP SDUforwarded by the first user equipment to the second user equipment.

In some embodiments, the status report includes fourth information. Thefourth information is a sequence number SN of the first lost PDCP SDU inthe at least one PDCP SDU forwarded by the first user equipment to thesecond user equipment; or the fourth information is a sequence number SNof the first PDCP SDU that is not received by the second user equipmentand that is in the at least one PDCP SDU forwarded by the first userequipment to the second user equipment.

Further, the status report further includes fifth information, and thefifth information is used to indicate a receiving status of a PDCP SDUafter the first lost PDCP SDU or a receiving status of a PDCP SDU afterthe first PDCP SDU that is not received by the second user equipment.

In addition, the status report is generated by the PDCP of the seconduser equipment.

According to the data receiving status reporting method provided in thisembodiment, when there is a non-direct path between the remote UE andthe base station, the base station sends at least one data packet to theremote UE by using relay UE, and the relay UE determines a status ofreceiving the at least one data packet by the remote UE, and reports, tothe base station, the status of receiving the at least one data packetby the remote UE. When there is a direct path between the remote UE andthe base station, the base station may retransmit, to the remote UEbased on the status of receiving the at least one data packet by theremote UE, a data packet that is in the at least one data packet andthat is not successfully received by the remote UE. In a prior artapproach, a status report fed back by the relay UE to the base stationcan reflect only a status of receiving the at least one data packet bythe relay UE. If a packet loss occurs on a transmission path between therelay UE and the remote UE, the status report cannot reflect a realstatus of receiving the at least one data packet by the remote UE.However, in this example embodiment, the status report that is fed backby the relay UE and that is received by the base station may trulyreflect the status of receiving the at least one data packet by theremote UE, so that the base station retransmits a data packet to theremote UE based on the status report, and the remote UE receives, beforereceiving a lost data packet in the at least one data packet, a datapacket after the at least one data packet transmitted by the basestation. In this way, out-of-order receiving by the remote UE isavoided.

The foregoing mainly describes the solutions provided in the exampleembodiments from the perspective of interaction between networkelements. It can be understood that, to implement the forego ngfunctions, the apparatus in the example embodiments includes acorresponding hardware structure and/or software module for executingeach function. A person skilled in the art will understand that, incombination with units and algorithm steps of the examples described inthe embodiments disclosed in this specification, the embodiments hereinmay be implemented by using hardware or a combination of hardware andcomputer software. Whether a function is performed by hardware orhardware driven by computer software depends on particular applicationsand design constraints of the technical solutions. A person skilled inthe art may use different methods to implement the described functionsfor each particular application, but it should not be considered thatthe implementation goes beyond the scope of this disclosure.

In the embodiments of this application, the apparatus may be dividedinto function modules based on the foregoing method examples. Forexample, each function module may be obtained through division based oneach corresponding function, or two or more functions may be integratedinto one processing module or component. The integrated module may beimplemented in a form of hardware, or may be implemented in a form of asoftware function module. It should be noted that module division in theembodiments of this application is an example and is merely logicalfunction division. During implementation, there may be another divisionmanner.

When each function module is obtained through division based on eachcorresponding function, FIG. 10 is a possible schematic compositiondiagram of the apparatus (disposed in the first user equipment) in theforegoing embodiment. As shown in FIG. 10 , the apparatus may include adeterminer 301 and a transmitter 302.

The determiner 301 is configured to support the apparatus in performingstep 103 in the data receiving status reporting method shown in FIG. 5 .

The transmitter 302 is configured to support the apparatus in performingstep 104 in the data receiving status reporting method shown in FIG. 5 .

It should be noted that all related content of the steps in the methodembodiments may be cited in function descriptions of the correspondingfunction modules, and details are not described herein again.

The apparatus provided in this embodiment is configured to perform theforegoing data receiving status reporting method, and therefore aneffect the same as that of the foregoing data receiving status reportingmethod can be achieved.

When an integrated unit is used, FIG. 11 is another possible schematiccomposition diagram of the apparatus in the foregoing embodiment. Asshown in FIG. 11 , the apparatus includes a processor 401 and acommunicator 402.

The processor 401 is configured to control and manage an action of aserver. For example, the processor 301 is configured to support theapparatus in performing step 103 in FIG. 6 and/or another process of thetechnology described in this specification. The communicator 402 isconfigured to support the apparatus in communicating with anothernetwork entity, for example, communicating with the remote UE (remoteUE, namely, the second user equipment in the embodiments) or the basestation shown in FIG. 1 . The apparatus may further include a storage403, configured to store program code and data of the server.

The processor 401 may be a processor or a controller. The processor 401may implement or execute various example logical blocks, modules, andcircuits described with reference to content disclosed herein. Theprocessor may be alternatively a combination that implements acalculation function, for example, including one microprocessor or acombination of a plurality of microprocessors, or a combination of a DSPand a microprocessor. The communicator 402 may be a transceiver, atransceiver circuit, a communications interface, or the like. Thestorage 403 may be a memory.

When the processor 401 is a processor, the communicator 402 is acommunications interface. When the storage 403 is a memory, theapparatus in this embodiment of this application may be the apparatusshown in FIG. 4 .

When each function module is obtained through division based on eachcorresponding function, FIG. 12 is a possible schematic compositiondiagram of the apparatus of the second user equipment in the foregoingembodiment. As shown in FIG. 12 , the apparatus may include a determiner501 and a sender 502.

The determiner 501 is configured to support the apparatus in performingstep 203 in the data receiving status reporting method shown in FIG. 9 .

The sender 502 is configured to support the apparatus in performing step204 in the data receiving, status reporting method shown in FIG. 9 .

It should be noted that all related content of the steps in the methodembodiments may be cited in function descriptions of the correspondingfunction modules, and details are not described herein again.

The apparatus provided in this embodiment is configured to perform theforegoing data receiving status reporting method, and therefore aneffect the same as that of the foregoing data receiving status reportingmethod can be achieved.

When an integrated unit is used, FIG. 13 is another possible schematiccomposition diagram of the apparatus disposed in the second userequipment in the foregoing embodiment. As shown in FIG. 13 , theapparatus includes a processor 601 and a communicator 602.

The processor 601 is configured to control and manage an action of theapparatus. The communicator 602 is configured to support the apparatusin communicating with another network entity, for example, communicatingwith the base station or the relay UE shown in FIG. 1 . The apparatusmay further include a storage 603, configured to store program code anddata of the apparatus.

The processor 601 may be a processor or a controller. The processor 601may implement or execute various example logical blocks, modules, andcircuits described with reference to content disclosed in thisapplication. The processor 601 may be alternatively comprise acombination that implements a calculation function, for example,including one microprocessor or a combination of a plurality ofmicroprocessors, or a combination of a DSP and a microprocessor. Thecommunicator 602 may be a transceiver, a transceiver circuit, acommunications interface, or the like. The storage 603 may be a memory.

When the processor 601 is a processor, the communicator 602 is atransceiver, and the storage 603 is a memory, the apparatus in thisembodiment of this application may be an apparatus shown in FIG. 14 . Asshown in FIG. 14 , the apparatus includes a processor 701, a memory 702,a communications interface 703, and a communications interface 704. Thecommunications interface 703 is configured to communicate with firstuser equipment (for example, the relay user equipment in thecommunications system shown in FIG. 1 ), and the communicationsinterface 704 is configured to communicate with a network device (forexample, the base station in the communications system shown in FIG. 1).

The foregoing descriptions about implementations allow a person skilledin the art to understand that, for the purpose of convenient and briefdescription, division of the foregoing function modules is used as anexample for illustration. In actual application, the foregoing functionscan be allocated to different modules and implemented according to animplementation constraint, that is, an inner stricture of an apparatusis divided into different function modules to implement all or some ofthe functions described above. For a detailed working process of theforegoing system, apparatus, and unit, refer to a corresponding processin the foregoing method embodiments. Further details are not describedherein.

In the several embodiments provided herein, it should be understood thatthe disclosed system, apparatus, and method may be implemented in otherways. For example, the described apparatus embodiment is only anexample. For example, the module or unit division is only logicalfunction division and may be other division in actual implementation.For example, a plurality of units or components may be combined orintegrated into another system, or some features may be ignored or notperformed. In addition, the displayed or discussed mutual couplings ordirect couplings or communication connections may be implemented byusing some interfaces. The indirect couplings or communicationconnections between the apparatuses or units may be implemented inelectronic, mechanical, or other firms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected based on actualrequirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of this application maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit. Theintegrated unit may be implemented in a form of hardware, or may beimplemented in a form of a software functional unit.

When the integrated unit is implemented in the form of a softwarefunctional unit and sold or used as an independent product, theintegrated unit may be stored in a non-transitory computer-readablestorage medium. Based on such an understanding, all or some of thetechnical solutions herein may be implemented in the form of a softwareproduct. The computer software product is stored in a non-transitorystorage medium and includes several instructions for instructing acomputer device (which may be a personal computer, a server, a networkdevice, or the like) or a processor to perform all or some of the stepsof the methods described in the embodiments of this application. Theforegoing storage medium includes: any medium that can store programcode, such as a flash memory, a removable hard disk, a read-only memory,a random access memory, a magnetic disk, or a compact disc.

The foregoing descriptions are merely specific example embodiments ofthis application, but are not intended to limit the protection scope ofthis patent. Any variation or replacement within the technical scopedisclosed herein shall fall within the protection scope of this patent.Therefore, the protection scope of this patent shall be defined by theclaims.

The invention claimed is:
 1. A method performed by second user equipment comprising: receiving at least one packet data convergence protocol layer (PDCP) protocol data unit (PDU) forwarded by first user equipment; determining a receiving status of the at least one PDCP PDU; and sending a status report to a network device indicating the status of receiving the at least one PDCP PDU by the second user equipment, wherein the status report comprises information indicating a sequence number SN of a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP sequence number SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number of the last PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of the last PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively in the at least one PDCP SDU; or the first information is used to indicate a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following the last PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively.
 2. The method of claim 1, wherein the at least one PDCP PDU is received via a radio bearer of a sidelink between the second user equipment and the first user equipment.
 3. The method of claim 2, wherein the radio bearer of the sidelink comprises an RLC (PC5) entity between the first user equipment and the second user equipment and a corresponding logical channel.
 4. The method of claim 1, wherein the received at least one PDCP PDU is carried in one or more RLC PDUs.
 5. The method of claim 1, wherein the sending the status report to a network device is triggered by a PDCP entity.
 6. The method of claim 1, wherein the status report is sent to the network device in response to an expiration of a timer.
 7. The method of claim 1, wherein the status report is sent to the network device in response to an indicator bit being a value triggering the status report.
 8. User equipment comprising: a receiver, configured to receive at least one packet data convergence protocol layer (PDCP) protocol data unit (PDU) forwarded by first user equipment; a processor, configured to determine a receiving status of the at least one PDCP PDU; and a transmitter, configured to send a status report to the network device indicating the status of receiving the at least one PDCP PDU by the second user equipment, wherein: the status report comprises information indicating a sequence number SN of a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP sequence number SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number of the last PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully forwarded by the first user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of the last PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively in the at least one PDCP SDU; or the first information is used to indicate a sequence number SN of a PDCP SDU following a PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively and that has a highest PDCP SN or a highest PDCP count value in the at least one PDCP SDU; or the status report comprises information indicating a sequence number SN of a PDCP SDU following the last PDCP SDU that is in PDCP SDUs successfully received by the second user equipment consecutively.
 9. The user equipment of claim 8, wherein the at least one PDCP PDU is received via a radio bearer of a sidelink between the second user equipment and the first user equipment.
 10. The user equipment of claim 9, wherein the radio bearer of the sidelink comprise an RLC (PC5) entity between the first user equipment and the second user equipment and a corresponding logical channel.
 11. The user equipment of claim 8, wherein the received at least one PDCP PDU is carried in one or more RLC PDUs.
 12. The user equipment of claim 8, wherein the sending the status report to a network device is triggered by a PDCP entity.
 13. The user equipment of claim 8, wherein the status report is sent to the network device in response to an expiration of a timer.
 14. The user equipment of claim 8, wherein the status report is sent to the network device in response to an indicator bit being a value triggering the status report. 